COMPRESSION COATED TABLETS AS DRUG DELIVERY SYSTEM … COATED TABLETS AS DRUG... · COMPRESSION...

IJPRD, 2014; Vol 6(01): March-2014 (021 - 033) International Standard Serial Number 0974 – 9446

Available online on www.ijprd.com

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COMPRESSION COATED TABLETS AS DRUG DELIVERY SYSTEM (TABLET IN TABLET ) : A REVIEW

Rohit Pawar1*

,

Manish Jaimini1, Bhupendra S. Chauhan

1, Sanjay K. Sharma

1

1Department of pharmaceutics, Jaipur college of pharmacy, Jaipur.

ABSTRACT

Tablets are the most preferred and widely used dosage form

because of their ease of administration, lower cost of

manufacture, and elegance. So in this article, we describe the

general characteristics, introduction,classification and formulation

consideration of compression coating tablet. The compression-

coating granulation or blend can be preformulated to provide

desired functionalities to the coating. The only requirement for

producing the compression-coated tablet dosage form described

herein is that the core material should possess the ability to flow

into a die during production.In past few years, chemical entity

often is first formulated as a free-flowing granulation for

encapsulation within hard gelatin capsules. Very conventional

ideas has been used for the deployment of the drug likewise single

dosage form with API and excipient, one dosage form for only one

disease etc. so duration of course and treatment of the disease

maximized.So for the minimization of that there are number of

innovations and new approach has been profound.

Keywords: Compression coated tablet,inlay tablet ,OSDRC, Tablet

in tablet technology.

INTRODUCTION

Pharmaceutical coatings are an essential tool to

achieve the desired formulation of pharmaceutical

dosage forms.Coatings are applied to achieve

superior aesthetic property of a dosage form (e.g.

color, texture, mouth feel and taste masking),

physical and chemical protection for the drugs in

cores, and modified drug release characteristics.

Coating techniques mostly used in pharmaceutical

industry are aqueous or organic coating, which

present some disadvantages: time consuming,

stability for heat labile and hydrolysis of

degradable drug and polluted environment

problem. Thereby, non-solvent coating is

introduced as alternative coating technique to

overcome these disadvantages. Non-solvent

coatings have been categorized as press coating,

hot melt coating, supercritical fluid spray coating,

Correspondence to Author

Rohit Pawar

Department of pharmaceutics, Jaipur

college of pharmacy, Jaipur,

Rajasthan, India

Email: [email protected]

International Journal of Pharmaceutical Research & Development ISSN: 0974 – 9446


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electrostatic coating, dry powder coating and

photocurable coating [1]

. Among these techniques,

compression coating is the absolute dry coating

without solvent and heat use. Aditionally

compression coating has no limitation for the cores

and hence overcomes the adhesion problem found

in spraying methods. Tablets with cylinder or

special shapes can be press-coated.

Tablet-in-tablet technology: Tablets are indeed the

most popular solid dosage form for oral

administration. One category of tablet

formulations that has gained remarkable

importance in drug therapeutics owing to various

benefits it offers is controlled or modified release

formulations. Although less popular, tablet-in-a-

tablet technology (see Fig 1) gained increased

interest in the recent years for creating modified

released products. It involves the compaction of

granular materials around a preformed tablet core

using specially designed tableting equipment.

Compression coating is a dry process. This type of

tablet (compression coated tablet) has two parts,

internal core and surrounding coat. The core is

small porous tablet and prepared on one turret.

After tablet core manufacture it is transferred

(centrally positioned) to another slightly larger die

that is partially filled with coating powder. More

coating powder is filled on the top of the core and

compressed again resulting in tablet with in tablet.

Mechanically, it is a complex process, as the tablet

may be tilted when transferred to the second die

cavity. Mostly, the coat is water soluble and

disintegrates easily after swallowing, in order to

achieve immediate release product. This tablet

readily lend itself in to a repeat action tablet as the

outer layer provides the initial dose while the inner

core release the drug later on. But, when the core

quickly releases the drug, entirely different blood

level is achieved with the risk of over dose toxicity.

To avoid immediate release of both the layers, the

core tablet is coated with enteric polymer so that it

will not release the drug in stomach while, the first

dose is added in outer sugar coating. Even so,

coating operation requires interpretation while

manufacturing and dawdling the manufacturing

process. Sometimes, inner core may be of liquid

formulation to provide immediate release of core

after the coat gets dissolved.[2]

FIGURE 1 (a) : TABLET-IN-TABLET TECHNOLOGY

FIGURE 1 (b): TABLET-IN-A-TABLET TECHNOLOGY



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Advantages of tablet-in-a-tablet technology

� It is simple and inexpensive.

� It is used to separate incompatible materials

(one in the core and the other in the coat).

� May be used to create modified-release

products such as Delayed Release (Release in

Intestinal).

� It is not hazardous to the environment since it

does not require the use of high amounts

of organic solvents.

� Compression coated tablet (CCT) can also be

used to avoid pharmacokinetic drug–drug

interactions between concomitantly

administered medications, creating a time

interval between their releases into the

gastrointestinal tract.[3]

CLASSIFICATION OF COMPRESSION-COATED

TABLETS BASED ON CORE SURFACE COATING:

The application of compressed polymeric coat on

tablets for modified or controlled drug delivery

systems have been developed and investigated to

improve the performance of drugs, to increase the

pharmacological effect and reduce side effects.

Based on the simplest matrix device where the

drug is homogenously dispersed in the polymer

network. If surface of cores is partially coated with

different properties of polymer, a variety of

modified or controlled release can be obtained [4,5]

.

The preparation development based on this

concept can improve or adjust the drug release in a

desired manner. A compression-coated tablet is a

system in which the all surface of an inner core is

completely surrounded by coat. These coats

prevent drug release from the core until the

polymeric coat is entirely eroded, dissolved or

removed (breaking down). Different drug release

fashion could be obtained depending on coating

layer and core composition.

A) Controlled release systems from compression-

coated tablets :Compression-coated tablet consists

of a core (fast disintegration or modified release)

which is coated by compression with a solid

barrier. The barrier could contain polymeric

material, diluent (as a release modifier) and drug

(for extended release). Compression-coated tablets

could be modulated to provide different release

patterns depending on the drug distribution and

plus with different type of controlling polymer used

in core and coat. Based on this concept, the

possibly obtainable modified drug releases are

extended release and delayed release (time, pH

and microbially control) for specific region of

gastrointestinal tract.

B) Multiphasic release : Multiphasic release is a

delivery system designed for many diseases which

have marked diurnal rhythms, while constant drug

release does not meet the optimum therapeutic

efficiency. In such diseases, drug concentrations

are needed to vary during the day. Drug levels

need to be highest when symptoms are most

severe. In the system, drug is presented in coat and

core as a non uniform drug distribution matrix

which results in biphasic drug release With the

combination of therapeutic drugs in one tablet, a

variety of drug release: sequential release of

different drugs or multi-phasic release of drugs is

achievable. Compression-coated tablets with

multiple layers for desirable therapeutic use can be

prepared. Multiple layer compression-coated

tablets containing immediate release (outer coat),

extended release (middle coat) and immediate

release (core), have been patented by Impax

Pharmaceuticals Inc.. Different drug release

patterns can be obtained with adjusting drug

loading and polymer type in each layer.[6]

C) Delayed release : Delayed release, defined with

lag phase and followed with release phase, is

obtained when all surface of core is compression-

coated. Pulsatile release defined by fast drug

release after a certain lag time could be

categorized within this group as well. Lag time for

drug release could be controlled by the application

of different polymeric coats which were

differentiated with triggering factors to control

drug release as mainly mentioned in colonic drug

delivery system.[7]

D) Time controlled release: A delayed release

tablet consists of a drug core which is compression-

coated with different polymeric (pH independent)

barriers. This delayed drug release is programmed

for the treatment of disease that depends on



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circadian rhythms. The lag time of drug release is

controlled by the compression coating, which

prevents drug release from the core until the

polymer coat is completely eroded, swollen or

ruptured. Drug release pattern depends on the

compression-coat properties. The press-coating

could be performed with water soluble polymers

(hydroxypropylcellulose, hydroxylpropyl-

methylcellulose, pectin, polyethylene oxide), water

insoluble polymer (ethylcellulose) and wax

(Behenic acid). Verapamil HCl tablets with floating-

pulsatile release properties were prepared by

compression coating of the drug core in an

hydroxylpropylmethylcellulose compression-coat.7.

Type and amount of salts and surfactants can

control the lag time of drug release by changing the

solubility of this polymer. The influence of both

could be explained by lowering the critical point

solution temperature (LCST) or inverse phase

transition temperature of the polymer. As the

temperature increases beyond the LCST, polymer

become insoluble and phase separation occurs.

Below this temperature, the polymer is soluble in

aqueous media and the polymer chains are

extended and surrounded by water.[8]

E) pH controlled release : A delayed release

system using enteric polymers as a coating can

provide site-specific drug delivery especially for

colon. This system has attracted a great interest for

the local treatment of a variety of bowel diseases

and for improving systemic absorption of

therapeutic agents susceptible to enzyme digestion

in the upper gastrointestinal (GI) tract, while time

controlled release can not achieve owing to large

variations in gastric emptying time. Fukui et al.

(2001a) have prepared the compression-coated

tablets of diltiazem hydrochloride intended for the

colon targeting[.9]

.

F) Microbial controlled release: A delayed release

system may be aimed for colon drug targeting. This

system is based on the degradation of the

polymeric compression-coat by specific enzymes

produced by entero-bacteria in the colon.

Microbially degradable polysaccharides containing

glycosidic bonds such as alginates, amylase,

arabinogalactan, arabinoxylan, cellulose, chitosan,

chondroitin sulfate, dextran, galactomannan (guar

gum, locust bean gum), inulin, karaya gum,

laminarin, pectins, starch, tragacanth gum, xanthan

gum and xylan, could be employed as a coat. The

investigated polysaccharides used for colonic-

specific drug delivery which could also be used in

compression-coated tablets included high methoxy

pectin [10]

, pectin plus HPMC [11]

. Combination of

time (pH) and bacterially controlled systems by

using of spray-dried chitosan acetate and ethyl

cellulose was investigated, .

FACTORS AFFECTING ON THE DRUG RELEASE

A) Tablet cores

a) Drug solubility: Higher solubility drug containing

cores in compression-coated tablets provided

shorter lag time than lower solubility drug

containing cores. Rapidly and completely release of

diclofenac sodium and salbutamol sulfate was

presented, while theophylline anhydrous exhibited

fast release and curved down after 60%. The partial

transformation of theophylline anhydrous to

theophylline hydrate was their explanation for the

retardation release behavior. The effect of drug

solubility: diclofenac sodium, theophylline

anhydrous and salbutamol sulfate in cores

containing sodium starch glycolate (50% of drug) as

disintegrant and ethylcellulose (fined powder) was

used as the compression-coat, [12]

.

b) Tablet core formulation: The higher solubility of

spray-dried lactose and HPMC facilitated the

dissolution in the core to make a faster

disintegration time and a shorter lag time. The

compression-coated tablets containing the same

coat but different cores showed identical in vitro

release profile but they were different in the

bioavailability. The in vivo results (the area under

the curve of acetaminophen plasma

concentration–time) revealed that compression-

coated tablets having larger core erosion could

provide the higher drug absorption from the GI

tract. Soluble diluent and appropriate amount of

super disintegrant in core tablets enhanced drug

release while osmotic agent slightly retarded drug

release.Drug release from compression-coated

tablet containing a fast release core was faster



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than extended release core containing coated

tablet when the same coating composition was

used [13]

. The release behavior and the lag time

were dependent on the type of excipient used in

the core.

B) Compression coating

a) Polymer type : The pharmaceutical polymers

used (single or combination) in compression

coating are cellulose derivatives

(e.g.hydroxypropylmethylcellulose

acetatesuccinate, ethylcellulose

,hydroxypropylmethylcellulose,

hydroxypropylcellulose and hydroxyethyl-

cellulose), polysaccharides (e.g. guar gum, sodium

alginate and pectin),water soluble polymer

(polyethylene oxide) and wax (behenic acid) and

methacrylate copolymers .The coats containing

these polymers could be divided into groups such

as water insoluble (ethylcellulose),erodible (low

molecular weight hydroxypropylmethyl-cellulose,

hydroxypropylcellulose, polyethylene

oxide),gellable or swellable (high molecular weight

hydroxypropylmethylcellulose),pH dependent

soluble (hydroxypropyl-methylcellulose acetate

succinate, methacylic acid copolymer),waxy and

bacterial digestible.The properties of these

polymers control drug release in different manners

as previously mentioned. Poly (N-isopropyl

acrylamide) was used as compression-coat. The

delayed release of drug was controlled by the type

and the amount of salt incorporated in the core.

This was attributed to the effect of lowering the

LCST (lower critical point solution temperature) or

inverse phase transition temperature of the

polymer by the added salt. As the temperature

increased beyond the LCST, polymer became

insoluble and phase separation occurred. Below

this temperature, the polymer was soluble in

aqueous media and the polymer chains were

extended and surrounded by water. Conte et al.

(1993) showed that the release behavior from

compression-coated tablets was controlled and

modulated by type and molecular weight of the

polymer used as shell [14]

.

b) Particle size of polymer used: Compression-

coated tablets prepared with smaller particles sizes

of ethylcellulose provided longer lag time.

compression-coated tablets prepared with smaller

particles sizes of ethylcellulose provided longer lag

time. The smaller particle size of ethyl cellulose

used in coat provided less porosity and higher

tortuous path for medium infiltration, then the

longer lag time of drug release was obtained. Lag

time of compression-coated tablets containing

ethylcellulose mixtures (granules and fine powder,

1:1) as coat was only slightly different from tablets

containing fine powder as coat because fine

ethylcellulose powder was filled the inter- and

intraparticulate gaps of coarse ethylcellulose

powder. The influence of particle size of coating

material in form of granules was more pronounced

than in form of powder.Compression-coated

tablets from granulated coat provided faster drug

release and shorter lag time compared to tablets

from fine powder coat. Different lag time and drug

release mechanism of ethyl-cellulose compression-

coated tablets were illustrated by incorporation of

different excipients into the upper coat of

compression-coated tablets with the same lower

coat, ethylcellulose coarse powder [15]

. (Fig. 2).



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FIGURE 2 : schematic dissolution process for drug

release from compression-coated tablets

containing the same lower compression-coat

(ethylcellulose coarse powder) and different upper

compression-coats: (a) ec coarse powder and ec

fine powder = 6:1; (b) ethylcellulose coarse powder

and explotab = 6:1; (c) ec coarse powder and avicel

= 6:1; (d) ethylcellulose coarse powder and

hydroxylpropylmethyl-cellulose = 6:1; (e)

ethylcellulose coarse powder and spray dried

lactose = 6:1; (f) ethylcellulose coarse powder and

dibasic calcium phosphate = 6:1 [16]

.

c) Porosity or release modifier incorporated in

coat : When hydrophilic excipients are

incorporated into an insoluble coating, they

possibly act as a pore-forming agent for water

penetration and the higher content of water

soluble excipient in the coating results in shorter

lag time. Different release behaviors from

compression-coated tablets containing different

hydrophilic excipients were resulted from different

physiochemical properties. For compression-

coated tablets comprising cores in impermeable

cup devices with modified surface matrix layer, the

lag time for drug release was controlled by varying

the ratio of water soluble diluent (lactose) and

behenic acid in surface layer. A higher ratio of

lactose to behenic acid resulted in shorter lag time

of drug release obtained. This could be attributed

to the more porous after lactose leakage or less

tortuous surface layer.The lag time from press-

coated tablets containing an

ethylcellulose/hydroxypropyl-methylcellulose E4M

shell was longer when compared with



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ethylcellulose/spray dried lactose shell due to

higher water solubility of the latter [17]

.

d) Core-coat ratio : For the time controlled release

system from compression-coated tablets, the

amount of the outer shell is a key factor for

controlling the lag time. Higher amount of the

outer coating added would prolong the lag time of

drug release.Insufficient polymer amount of coat

would result in absent of the lag time, since the

drug might be released through the incomplete

form of ethylcellulose compression-coat. For

insoluble polymer coat like ethyl cellulose, the

influence of polymer amount or thickness of coat

onthe lag time and drug release was

investigated.[17]

.

e) Compression force : Absence of compression

force effect on drug release was found when the

compression force for coating was constant. In

addition, the influence of compression force

applied to the coat on the drug release of

ethylcellulose compression-coated tablets was

presented. When an insoluble coat is applied on a

core with different compression forces, the lag

time and drug release rate will be modified. The lag

time of drug release increased and the release rate

decreased when the compression force applied to

the coating increased till a critical point. Their

result could be explained by a decrease of coat

porosity with higher compression forces leading to

slower diffusion or lower permeability of water

through the porous polymer matrix as compression

coat Higher compression force applied in

compression coating leading to lesser porosity in

the coat results in longer lag time. The effect of

compression force applied to inner core on drug

release from ethylcellulose compression-coated

tablet was studied.[17]

FORMULATION CONSIDERATION OF

COMPRESSION-COATING TECHNIQUE :

A) Compression-coating amount : Coating amount

is the most important parameter to achieve a

coating uniform for compression-coated tablets. A

compression-coated tablet requires a coating

which is about twice the weight of the core or,

more general, the volume must be greater than

that of the core itself. If the cores are comprised

mainly of low density materials, such as fats and

waxes, the amount or weight of coating must be

even greater to assure a uniform volume of coating

material for covering the core and adhesion of core

and coating. Recently, increasing the drug loading

by decreasing the compression coat could be

performed with a novel compression tool (one-step

dry coated tablet manufacturing method; OSDRC-

system) [18]

.

B) Position of core in coated layer : The main

drawback of this system is the centralization of

core in the compression-coated tablets. The

reproducibility of drug release from compression-

coated tablet is questionable, since the faults of

press-coating can happen. Examples of press-

coating fault are unequal coating, cocking and off-

center. However, this drawback has been recently

overcome by the novel compression tools (OSDRC-

system) which placed a core in a certain position.

X-ray computed tomography as non-invasive and

rapid characterization method in online processing

control for press-coated tablets. This technique

provided cross-sectional images, which can be

accumulated and built up three-dimensional

images. This is based on the difference in X-ray

transmittance, depended on the density of the

tablet reflecting geometrical structure of

compressed tablets [19]

.

C) Compression force and Compressibility of

materials : The compressibility of coated tablets is

mainly depended on the coating material. Thus,

cohesiveness and plasticity of the powder coat are

needed to obtain satisfactory mechanical strength

of the coating. The cohesiveness indicates the

continuity of the coating around the edge of the

core, which depends on its strength and the

plasticity responses for the expansion of the core

after the final tablets are released from the die.

The final compression force applied to prepare

compression-coated tablets need to be higher than

the compression force which was applied to the

core, to ensure the adhesion between core and

coat. Tablets with adhesive coating can be applied

as core to ensure adhesion of compression coat

and core [20]

.



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D) Interaction between drug and compression

coat : The interaction of drug and coating is needed

to be considered when gellable compression coats

are used for drug release control. Drug in

compression-coated tablets diffuses through the

swollen coat. This process might enhance some

possible interaction between drug and coat. The

difference in drug release of the enantiomers of

verapamil hydrochloride from compression-coated

tablets containing chiral polymers (pectin,

galactomannan and scleroglucan) as the coat has

been found.[21].

RECENT TECHNOLOGIES USED IN COMPRESSION

COATING METHOD :

Compression coating technique has been described

as compressing a coat around a core using specially

designed processes. The process involves

preliminary compression of the core, which is then

transferred to a large die already containing some

(a half) coating material. After centralizing the

core, further coating material is added and the

whole compressed to form the compression-

coated tablets. The machines available for the

preparation of press-coated tablets fall into two

basic types: core previously prepared on other

machines; compression of core and coat in one

continuous circle.

A) OSDRC : A novel one-step dry coated tablet

manufacturing method (OSDRC-system) was

introduced. The OSDRC-system was capable of

producing compression-coated tablets in one

process without previous core tablet

preparation.The core and coat were prepared in

the schematic sequence of the OSDRC process (Fig.

3). First, the lower-outer layer was formed by pre-

compression from the upper-center punch. Then,

the lower-center punch was slid down and the

upper-center punch was moved up. The powder for

the core was filled and pre-compressed by the

upper-center punch. Finally, the lower-outer punch

was slid downward and the powder for the 2nd

outer layer was filled and compressed by the upper

and lower punches in which the center punches are

unified with the outer punches. This system can be

assembled onto the turn table of a rotary tableting

machine and can make a dry-coated tablet in a

single turn. By using the OSDRC-system,

compression-coated tablets with a side outer coat

thickness of 1 or 0.5 mm can prepared. [22 , 23]

FIGURE 3 :PROCESS OF OSDRC MANUFACTURING METHOD AS DESCRIBED.

B) Dividable compression-coated tablets : It

contains two cores in the controlled-release coat

were prepared [18]

,(Fig. 4). The aim of dividable

compressioon-coated tablets development was to



29

match the drug kinetics to individual patients (dose

adjustment). The feasibility of this dividable

control-released compression-coated tablet has

been illustrated with comparable drug release from

dividable and non-dividable compression-coated

tablets.

FIGURE 4 : MANUFACTURING PROCESS OF DIVIDABLE OSDRC

Compression-coated tablets in form of layer tablets

(doughnut-shaped) have been prepared by partial

compression coating technique using a specially

designed punch set. The production process of the

Manesty F3 for the three-layered tablets is shown

as schematic diagram in Fig. 5 [24]

.

FIGURE 5 : SCHEMATIC DIAGRAM OF THE PROCESS OF THREE-LAYERED TABLETS ON THE MANESTY-F3

TABLETING PRESS.

C) INLAY TABLETS : A type of layered tablet in

which instead the core tablet being completely

surrounded by coating, top surface is completely

exposed. Tablet compressing was done with core



30

rod tooling in which only one surface of core is

expose to outside and other drug is incorporated in

cup portion. While preparation, only the bottom of

the die cavity is filled with coating material and

core is placed upon it [25, 26]

.The main body portion

may consist of an uncoated granulation which is

compressed around the enteric coated inlay

portion In this modification the main body portion

of the tablet is first released and assimilated in the

gastrointestinal tract while the enteric coating

protects the inlay portion for a predetermined

period of time so as to provide time delayed or

sustained medication. Atoz is offering Inlay tablets

with combinations like Metformin 500mg sustained

release (Outer coat) and Pioglitazone 15 mg (core

tablet) which has a very unique advantage

FIGURE 6 : PREPARATION OF INLAY TABLETS.

a) Advantages of inlay tablets

� Dosage form comprising of an active

ingredient as modified release and an active

ingredient as immediate release can be

prepared.

� Has the ability to release soluble and insoluble

drugs at a zero-order rate of release in

dissolution media .Dosage frequency of

highly water soluble drugs con be reduced

providing same efficacy.

� Tablets of different shape such as triangular,

rectangular, or capsule shaped tablets can be

manufactured.

� Adverse effects due to sub therapeutic plasma

concentration can be avoided.

� Plasma level can be maintained constant and

within the therapeutic window throughout the

period of treatment.

� The burst effect, namely, large release within a

short period of time, is common in highly

soluble drugs, and shall be avoided, as it may

lead to high concentration of active

ingredients in the blood stream.

Preparation Of The Compression-Coated (In-lay)

Tablets: A carefully weighed amount of powder

blend (coating blend) was placed in the die and

compressed on a Carver Press (Wabash, IN) at a

known force with the tooling shown in( Figure 7),

to produce a cup-shaped tablet (cup). The cup was

left within the die, and a known amount of either a

model drug or a blend containing the drug was

placed inside the cup and tamped lightly with the

punch in an extended position. A weighed

amount of the coating blend was placed on top of

the die contents, and the cup was compressed for a

second time with the punch in a retracted position



31

at a known force to produce the final compression-

coated tablets.

FIGURE 7 : PHOTO OF THE TOOLING USED TO DEMONSTRATE PROOF-OF-CONCEPT, A CUP, AND A FINISHED

DOSAGE FORM

Patented inlay tablet formulations. [27]

1.Pravastatin Sodium (10mg) + Niacin (500mg)

2.Pravastatin Sodium (10mg) + Niacin(1000mg)

3.Lamotrigine (25mg) + Sodium Valproate(500 mg)

4.Lamotrigine (25mg) + Sodium Valproate(1000

mg)

5.Rosiglitazone Maleate (2mg) + Metformin

Hydrochloride (500mg)







9.Glimipride (1mg) + Metformin Hydrochloride

(500mg)

10.Glimipride (2mg) + Metformin Hydrochloride

(500mg)

APPLICATION OF COMPRESSION COATING

TECHNIQUE IN PHARMACEUTICAL FORMULATION:

Compression coating, or press-coating, has been

introduced during the period 1950-1960 to

formulate incompatible drugs. This coating

became interesting in the last two decades owning

to the advantages over liquid coating, since the

process does not need the use of solvents, requires

a relatively short manufacturing process and allows

greater weight gain to the core tablet. Nowadays,

pharmaceutical aspects of compression-coated

tablets in dosage form development are:

(1) To protect hygroscopic, light-sensitive, oxygen

labile or acid-labile drugs;

(2) To separate incompatible drugs from each other

and achieve sustained release;

(3) To modify drug release pattern (delayed,

pulsatile and programmable release for different

drugs in one tablet).

However, some drawbacks of compression-coating

technique are:

(1) The requirement of reliable and reproducible

central positioning of the core tablet within

compression-coated tablet, the need of a multiple-

step process or a special tableting machine.

Recently, the common manufacturing problems for

compression-coated tablets, such as central



32

positioning of the core in the compression-coated

tablets and absence of core in coat, have been

overcome by applying a novel one-step dry coated

tablet (OSDRC) method .The OSDRC system has

been introduced to improve tableting of low

compressible material (such as acetaminophen) as

the core, with no diluents by using high tablet

ability excipient as the coat. The radial tensile

strength of OSDRC tablets was the same or

superior to that of physical mixture tablets.

However, the advantage of OSDRC compared to

physical mixture in term of drug loading has not

been mentioned. A novel sugar coating method by

compression using OSDRC system for moisture

protection has been introduced [28]

. The uses of

compression coating technique in controlled

release drug delivery systems have been recently

published. pH independent matrix tablets

containing a weakly basic drug with controlled

microenvironmental pH was studied. The release of

soluble pH modifiers out of tablet cores was

retarded by compression coating technique, when

compared to normal matrix tablet. In this case,

compression-coated tablets, which contained a

core of succinic acid as a pH modifier reservoir and

a coat of dipyridamole, HPMC K100 and succinic

acid, could successfully increase the release of the

weakly basic drug in higher pH medium by reducing

the microenvironment pH in the matrix coat.[29],.

CONCLUSION :

The compression coating technique can be applied

to obtain flexible drug delivery systems; modified

extended release with multiphase pattern and

delayed release (based on time controlled, pH

controlled and bacterial degradable controlled

release). Drug release of compression-coated

tablets as extended release can be modified by the

adjusting drug-polymer ratio in core and coat. For

the delayed release system, lag phase and release

phase can be modulated by changing the release

controlling parameters (polymer type, particle size

of polymer used, pore modifier, compression

coating thickness or core and coat ratio,

compression force) to achieve programmable drug

release for chronotherapy or site specific drug

delivery in GI tract. With a novel tableting

technology (high precision and accuracy) to

position core tablet in the center of the

compression-coat, the application of compression-

coated tablets as a tool for desirable drug release

control is feasible also in industrial scale.

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